MOULT 599 



The subject of Additional Moult is thus intimately connected 

 ■with the seasonal adornment of Birds, and as that properly be- 

 longs to a branch of the great question of Natural Selection it 

 could not be suitably entered upon here. The reader is accordingly 

 referred to those excellent chapters in which Mr. Darwin^ has 

 treated the matter with his usual perspicuity, though even he has 

 far from exhausted its varied points of interest. 



It remains to be remarked that though the annual Moult com- 

 monly takes place so soon as the breeding-season is over, there are 

 plenty of cases in which the change is delayed to a later period. 

 This is so with the Swallow, Hirundo rustica, which has long been 

 known to moult in our mid-wanter or even later, and it is generally 

 the way with the Diurnal Birds-of-Prey. But unquestionably most 

 birds accomplish the change much earlier, and before they leave 

 their breeding-quarters for their winter haunts, thereby starting on 

 one of their great annual journeys with all the external machinery 

 of flight renewed and in the best condition for escaping its attend- 

 ant perils. 



But the plumage is not the only part of the Bird's integument 

 that undergoes regularly periodical change. Many years ago 

 Nilsson made known by a communication to the annual report of 

 the Academy of Sciences of Stockholm on Zoology for 1828 (pp. 

 104-106) that in certain species of Tetraonidx (Grouse) the Claws 

 grow to an inordinate length in winter and are partly shed or worn 

 off as spring comes on, and the fact has since received further 

 attention (cf. Dresser, B. Eur. vii. p. 189, pi. 485). The seasonal 

 elongation of the bill of Redpolls during summer, first announced 

 as a conjecture by Gloger {Journ. fiir Orn. 1856, pp. 433-440), had 

 been previously made known to the present writer by Wolley, who 

 first observed it in 1853-4 (cf. Yarrell, Br. B. ed. 4, ii. p. 139). 

 In both these cases, however, the getting rid of the extraneous 

 growth is to a great extent a mechanical process, and therefore in 

 some measure comparable with the shedding of the fringes of the 

 feathers before mentioned. Not so does it seem to be with others, 

 and a far stranger state of things was revealed by the observation, 

 originally made by Mr. H. G. Palmer about 1865, according to Mr. 

 Eidgway (U. S. Geol. Explor. iOth Farall. iv. p. 634), who himself 

 confirmed it in countless instances, that irrespective of sex the 

 White Pelican of North America, during the breeding- season, 

 bears on the ridge of its bill a curious horny projection, flattened 

 at the sides and roughly-triangular in shape, which is worn for 

 about two months only, and then dropping ofi" may be " gathered 

 by the bushel " on the nesting-grounds of the species, as recorded 

 by Baird (Ibis, 1869, p. 350). Still more extraordinary was the 



^ The Descent of Man and Selection in relation to Sex, chaps, xiii.-xvi. 

 London: 1871. 



